1. Field of the Invention
The invention relates to a device for winding an inner coil of a transformer, the transformer of the inner coil including a ferrite core with an inner groove for receiving the coil, the ferrite core being provided with a radial inlet groove for feeding in and feeding out of the winding wire.
2. Description of the Prior Art
It is known in the prior art to employ rotating head wheels with one or a plurality of heads in video recorders or recorder for digital recording and replay of signals to or from a magnetic tape. Thereby the signals are recorded by means of oblique tracks on the magnetic tape. It is further known to employ rotary transformers to communicate the signals between a head wheel and the stationary part of a head drum. These rotary transformers typically include a stationary part which is associated with the stationary head drum and a part associated with the rotating head wheel and rotating therewith. Both the stationary and the moving parts include a coil. A head drum arrangement must have as many transformers as there are heads on the head wheel.
For example, the use of such transformers is disclosed in laid open patent DE-A1-38 10 037. The transformers disclosed therein include inner and outer ferrite cores, each of which include a coil. The signal transformation and communication is performed radially between the ferrite cores mounted in the outermost stationary part and the ones mounted in the inner rotating part.
Due to the miniaturization of head drum units as well as the increased frequency range to be handled and due to the increased numbers of transformers, the size of the transformers must be reduced. This results in higher accuracy requirements for the transformers. This concerns the ferrite cores themselves to a certain extent, for example, the slot between the outer and inner core and, on the other hand, the coils. The coils of a very thin wire (for example, at a magnitude of 0.15 mm. diameter) must be wound very accurately in a very tight space. In order to mount a coil of a specific defined shape in a ferrite core, supporting auxiliary means may be used.
A rotary transformer for a recorder is disclosed in DE-A1-38 31 721 which employs a radially acting transformer. In this case, a plastic core with grooves is employed for the accurate guiding of the wire winding, which can be easily made and which assures a high degree of accuracy of the winding of the coil.
However, the use of such an auxiliary means is rather expensive. Moreover, the handling of a plastic core of such small dimension is also very difficult.
The placement of coils directly into a winding groove of ferrite core of an axial transformer is disclosed in DE-A1-36 26 275. With this device, a wire coil is wound in an axial groove in the plane surface of a ferrite core. This is performed with the assistance of a rotating winding disk which is mounted concentrically to the ferrite core, into which the winding wire is introduced through a guide slot. The purpose of this device is to replace preassembled coils which cannot be inserted into the winding groove because of large tolerances.